Electronic pills are ingestible capsules with electronic control circuitry to dispense medicine for therapeutic treatment during traversal of the alimentary tract. An electronic pill generally comprises a medicine reservoir, a dispensing opening, and a pump for transporting the medicine from the reservoir to the dispensing opening. Generally, the electronic pill also comprises control means to activate the dispensing pump at the desired moment, e.g. responsive to a signal from a sensor, such as a pH sensor which can be an integral part of the pill. After swallowing the pill is moved along the alimentary tract by the peristaltic movement of the muscles along the alimentary tract. During its travel through the intestines the pill drifts from the pylorus to the ileocaecal valve at about 1 m/hour. Due to the peristalsis of the small intestines superposed on the drift velocity, large velocity variations occur pushing the pill back and forth through the intestines. This way medication released from the pill is mixed thoroughly before it will be taken up through the wall of the intestines or becomes locally effective.
An example of an electronic pill is disclosed in WO 2006077529.
Hitherto, electronic pills are particularly suitable for dispensing liquid medicines. However, many medicines are in powder form. Medicines in powder form generally have better stability and shelf life. The problem is that dry powder exhibits elastic and plastic and viscous behavior. It is basically the mechanical strength of the particles that count. When tightly packed it behaves like an elastic body, requiring large mechanical loads to get it deformed. When the interactions between the particles of the powder are weaker than the mechanical strength of the powder particles, the packed powder behaves like an elastic plastic material. Under a certain value of the mechanical load the powder behaves like an elastic body, above that value it shows plastic behavior. When strongly agitated it acts like a fluid: the space between the particles of the powder are occupied by air or liquid and this causes that the powder particles can be easily displaced at low mechanical load. Due to this complex behavior of powders accurate metering and dispensing in miniature systems, such as electronic pills, is problematic.